Side reading reduced GMR for high track density

ABSTRACT

As track density requirements for disk drives have grown more aggressive, GMR devices have been pushed to narrower track widths to match the track pitch of the drive width. Narrower track widths degrade stability and can cause amplitude loss and side reading. This problem has been overcome by placing an additional layer of soft magnetic material on the conductive layer. The added layer prevents flux leakage into the gap region. A non-magnetic layer must be included to prevent exchange coupling to nearby magnetic layers. In at least one embodiment the conductive leads are used to accomplish this. A process for manufacturing the device is also described.

This is a divisional application of U.S. Ser. No. 10/856,181 filed onMay 28, 2004 now U.S. Pat. No. 7,203,039 which is a divisional of U.S.Ser. No. 10/135,097 filed on Apr. 30, 2002 (now issued as U.S. Pat. No.6,760,966), which are herein incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to the general field of read heads for magneticdisk systems with particular reference to flux leakage from the hardbias layers.

BACKGROUND OF THE INVENTION

The principle governing the operation of the read sensor in a magneticdisk storage device is the change of resistivity of certain materials inthe presence of a magnetic field (MR or magneto-resistance).Magneto-resistance can be significantly increased by means of astructure known as a spin valve. The resulting increase (known as Giantmagneto-resistance or GMR) derives from the fact that electrons in amagnetized solid are subject to significantly less scattering by thelattice when their own magnetization vectors (due to spin) are parallel(as opposed to anti-parallel) to the direction of magnetization of thesolid as a whole.

Referring now to FIG. 1, the key elements of what is termed a top spinvalve are, starting at the lowest level, seed layer 1, free magneticlayer 2, non-magnetic spacer layer 3, magnetically pinned layer 4,pinning layer 5, and capping layer 6. Inverted structures in which thefree layer is at the top are also possible (and are termed bottom spinvalves). To isolate the device from extraneous magnetic fields it issandwiched between two magnetic shields 11 and 17. Also seen in FIG. 1are the conductive leads 15 that attach to the device.

Although the layers enumerated above are all that is needed to producethe GMR effect, additional problems remain. In particular, there arecertain noise effects associated with such a structure. As first shownby Barkhausen in 1919, magnetization in a layer can be irregular becauseof reversible breaking of magnetic domain walls, leading to thephenomenon of Barkhausen noise. The solution to this problem has been toprovide a device structure conducive to single-domain films for the MRsensor and to ensure that the domain configuration remains unperturbedafter processing and fabrication steps and during normal head operation.This is most commonly accomplished by giving the structure a permanentlongitudinal bias provided by two opposing permanent magnets. In FIG. 1the longitudinal bias is provided by a laminate of ferromagnetic layer13 (typically nickel-iron) and antiferromagnetic layer 14. Analternative way to provide the longitudinal bias is to use a layer of amagnetically hard material. This is shown as layer 21 in FIG. 2.

As track density requirements for disk drives have grown moreaggressive, GMR devices have been pushed to narrower track widths tomatch the track pitch of the drive and to thinner free layers tomaintain high output in spite of the reduction in track width. Narrowertrack widths degrade stability as the device aspect ratio startssuffering. Thinner free layers have traditionally degraded stability andincreased the asymmetry distribution across the slider population.Hard-bias of the type described above, that is typically used toovercome stability concerns associated with the junction, also resultsin amplitude loss due to the field originating from the hard biasstructure. Side reading, which is attributable to any deviation of thehead microtrack profile from a square, also gets worse with narrowertrack widths

With increased track density, the dead zone (which is defined as thearea between the physical and magnetic read widths) in a conventionalcontiguous junction has been decreasing as the physical dimension hascontinued to shrink. At approximately 0.3 microns the dead zone becomesnegative implying that the magnetic read width (MRW) is larger than thephysical track width (PRW) dimension. Hence, for track width dimensionof 0.3 microns and less, it is possible to retain more than half thereadback amplitude with more than half the read head placed outside thewritten track.

This effect is due in part to the fact that the track width has beenscaling down faster than other dimensions such as shield-to-shield (S-S)spacing (18 a and 18 b) and fly height. Shown in FIGS. 1 and 2 are,respectively, typical exchange bias and hard bias contiguous junctionsin use with GMR devices. Modeling has shown that the side reading isreduced by using lower fly heights and thinner S-S. This implies thatpart of the side reading is due to the stripe edges and how they pick upflux from adjacent tracks. The topography for a typical head furtherincreases the S-S spacing at track edges since the shield to shield (18b) needs to be increased to accommodate the lead and stabilizationthickness.

A routine search of the prior art was performed with the followingreferences of interest being found:

In U.S. Pat. No. 6,198,608, Hong et al. show a contiguous junction GMRdevice. U.S. Pat. No. 5,818,685 (Thayamballi et al.) construct a biasingmagnet by using multiple layers of ferromagnetic material separated bynon-magnetic layers. U.S. Pat. No. 6,185, 078 B1 (Lin et al.) and U.S.Pat. No. 5,739,987 (Yuan et al.) are related MR processes.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a bottom spin valve having improved longitudinalbias relative to prior art devices.

Another object of at least one embodiment of the present invention hasbeen that said bottom spin valve exhibit minimal amplitude loss due tofields originating from the hard bias structure.

Still another object of at least one embodiment of the present inventionhas been that said bottom spin valve exhibit minimal side reading, evenwith narrower track widths.

A further object of at least one embodiment of the present invention hasbeen to provide a process for manufacturing said bottom spin valve.

These objects have been achieved by adding an additional layer of softmagnetic material above the hard biasing layer or layers. This layerprovides flux closure to the hard bias layers thereby preventing fluxleakage into the gap region. A non-magnetic layer must be included toprevent exchange coupling to the hard bias layers. In at least oneembodiment the conductive leads are used to accomplish this. A processfor manufacturing the device is also described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show read heads of the prior art that have less thanperfect longitudinal bias.

FIG. 3 shows a first embodiment of the invention.

FIG. 4 shows a second embodiment of the invention.

FIG. 5 shows a third embodiment of the invention.

FIG. 6 shows a fourth embodiment of the invention.

FIG. 7 shows a fifth embodiment of the invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention compensates for the improper scaling of the head,which was discussed earlier, by introducing additional shielding intothe lead structure. This is accomplished by depositing a thin NiFe layerwhose thickness is comparable to that of one or two of the aluminainsulators seen as 12 and 16 in all figures. The NiFe is placed betweenthe leads and the antiferromagnet and it conducts the flux from theadjacent track directly into the actual shields (upper and lower) ratherthan allowing it to be picked up by the GMR sensor. This additional NiFeis stabilized by the exchange bias structure that is used to stabilizethe device. Part of the excess flux from the tail is routed into thisadditional NiFe layer.

We now describe a process for manufacturing the present invention. Inthe course of this description, the structure of the present inventionwill also become apparent. Referring now to FIG. 3, the process beginswith the provision of lower magnetic shield 11 onto which is depositedinsulator layer 12. A bottom spin valve (layers 1-5 as discussedearlier) is then formed on insulator layer 12. As seen in the figure,capping layer 6 is centrally located directly above antiferromagnetic(pinning) layer 5. These layers are then shaped (usually by ion milling)so that they have two opposing sides that slope downwards and away fromcapping layer 6.

Next, in a first embodiment, nickel iron layer 13 is deposited on thesloping sides. This is followed by deposition onto 13 of secondantiferromagnetic layer 14 which is heated in a longitudinally orientedmagnetic field so as to provide permanent longitudinal bias to the spinvalve, as discussed earlier.

Now follows a key feature of the invention namely the deposition onto alayer 14 of non-magnetic layer 31, followed by the deposition of softNi—Fe layer 32 to a thickness between about 100 and 500 Angstroms, with300 Angstroms being preferred. The purpose of layer 31 is to eliminateany exchange coupling between layers 14 and 32 so its thickness isbetween about 25 and 100 Angstroms, with 50 Angstroms being preferred.The structure is then magnetized in a direction that is anti-parallel tothe magnetization direction of layer 13 by heating at a temperaturebetween about 180 and 280% C in a magnetic field of between about 500and 5,000 Oe for between about 0.5 and 5 hours. This added NiFe layerabsorbs flux from the recording medium when the data track is placedanywhere under the leads, preventing the side track information fromentering the GMR region thereby eliminating most of the side trackreading from adjacent tracks. Only when the data track gets close to thephysical track edge, the flux entering the GMR region starts gettingstronger. This leads to a magnetic read width closer to the physical andtherefore increases the dead zone, leading to a narrower track width.

Fabrication of the device is completed by depositing conductive leadlayer 15 on Ni—Fe layer 32, following which upper insulator layer 16 islaid down followed by upper magnetic shield 17.

Several variations on the above process are readily implemented. Asecond embodiment of the invention is illustrated in FIG. 4. It issimilar to the first embodiment described above in all respects exceptthat longitudinal bias is achieved by means of a single hard magneticlayer 21. Elimination of exchange coupling between layers 21 and 32 isstill required so non-magnetic layer 31 (thickness between about 25 and100 Angstroms, with 50 Angstroms being preferred) is still needed.

A third embodiment of the invention is illustrated in FIG. 5. Thisembodiment is similar to the first embodiment except that conductivelead layer 15 is deposited directly onto antiferromagnetic layer 15 withsoft Ni—Fe layer 32 being then deposited onto it. In this approach layer15 acts as the exchange decoupling layer so layer 31 is no longerneeded. The disadvantage (relative to the first embodiment) is therelatively larger distance between the soft NiFe layer and the physicaledge of the GMR sensor. The larger the distance the larger will be theside shielding effect and hence the increase in the dead zone. We notehere that layer 32 could also have been inserted into the middle oflayer 15 just so long as a sufficient thickness of to remove exchangecoupling is present.

The fourth embodiment that is shown in FIG. 6 also locates layer 32above the conductive leads (as in the third embodiment) but it achieveslongitudinal bias by means of hard magnetic layer 21 (as in the secondembodiment).

FIG. 7 shows a fifth embodiment in which free layer 71 of bottom spinvalve 72 is left intact under the antiferromagnet/ferromagnet bilayer14/13, separated therefrom by coupling layer 73. The latter is any oneof several metals such as Cu, Ag, Ru, or Rh and is between about 2 and20 Angstroms thick. Gap 74 defines the read width.

1. A magnetic read head, having a width, comprising: on a substrate, abottom spin valve whose topmost layer is a magnetically free layer onwhich is a magnetic coupling layer; on said magnetic coupling layer, afirst soft ferromagnetic layer on which is an antiferromagnetic layer;on said antiferromagnetic layer, a capping layer on which is aconductive lead layer; on said conductive layer, a second softferromagnetic layer; and a trench extending downward from said secondferromagnetic layer as far as said free layer, said trench having awidth that defines said read head width.
 2. The magnetic read headdescribed in claim 1 wherein said first soft ferromagnetic layer isbetween about 5 and 75 Angstroms thick and is selected from the groupconsisting of nickel-iron, cobalt-iron, cobalt, and nickel.
 3. Themagnetic read head described in claim 1 wherein said second softferromagnetic layer is between about 100 and 500 Angstroms thick and isselected from the group consisting of nickel-iron, cobalt-iron, cobalt,and nickel.
 4. The magnetic read head described in claim 1 wherein saidcoupling layer is between about 2 and 20 Angstroms thick and is selectedfrom the group consisting of Cu, Ag, Ru, and Rh.
 5. The magnetic readhead described in claim 1 wherein said read head width is between about0.05 and 0.2 microns.